Conventional pump systems for delivery of a fluid from a well bore include pump jacks or positive cavity pumps. While these pump systems have achieved extensive use, they suffer from many disadvantages. One disadvantage is that these systems are expensive. This is particularly problematic for wells with low delivery rates as the cost of the equipment may be difficult to justify. Further, these systems require the use of external power or fuel for use, which requires that power, or fuel be delivered to the well site. Again, the cost of providing power to a well having low delivery rate may be difficult to justify, particularly in remote well locations.
In order to overcome these problems, plunger lift systems have been employed for the delivery of fluid from a well head using pressure from the well. The fluid can include, for example, crude oil or gas. A typical plunger in use in a well bore has fluid above, which is being lifted from the well bore, and gas and fluid below, which is providing the pressure for lifting the plunger. Early plunger lift systems include solid rods without any sealing mechanism. The solid rod includes grooves that cause turbulence as gas passes the plunger in the well bore, which aids in lifting the plunger in the bore. These systems are not efficient, however, as they are prone to fluid and gas leakage past the plunger when in use. Escape of gas or fluid past the plunger causes a loss of gas and fluid pressure from below the tool which results in slower delivery of fluid to the top of the well bore.
Many variations to the plunger lift system have been proposed in an attempt to overcome these problems. For example, U.S. Pat. No. 6,148,923 to Casey, issued Nov. 21, 2000, teaches a plunger mechanism with a generally cylindrical body with an internal valve member and external seals. This plunger includes a tube, a detachable valve member that sits in the lower section of the tube and flapper sealing rings mounted along the tube. This plunger is allowed to fall down a well bore, the detachable valve member separates from the cylindrical body and falls independently through the well casing. Liquid passes through the center of the cylindrical body as the body falls. The detachable valve member strikes a stop in the well casing and the cylindrical body follows such that the valve member engages in the cylindrical body and forms a seal therein. Therefore, the liquid below the plunger is sealed from the liquid above the plunger and the plunger rises as a result of the pressure below.
The system disclosed by Casey suffers many disadvantages. This system is intended for use with a spring in the well bore for landing and cushioning of the auto cycle plunger. This spring can break down into pieces that can lodge in valves, flow lines or in the well bore and regular maintenance to avoid these problems can be costly. Also, the valve disclosed by Casey may not function well in certain environments. Without the use of a spring, for example, the ball may become lodged in sand or mud in the bottom of a well bore which may inhibit entry into the body of the plunger and prevent sealing. Furthermore, the flapper sealing rings are all urged in the downward direction as the plunger travels upwardly. When the head pressure rises above a critical pressure, the flapper sealing rings are not able to maintain a seal and fluid can escape past these sealing rings. Thus, the system disclosed by Casey is not effective in maintaining a seal below a perforation in a well bore. When the plunger is below a perforation, fluid pressure at the perforation acts downwardly on the plunger. If this pressure is too high, the sealing rings will not maintain a seal. Therefore this plunger is not effective in maintaining seal in a multiple perforated well bore (with more than one perforation in the well casing for fluid ingress into the well bore).
Accordingly, it is an object of the present invention to provide a plunger for delivery of fluid to the top of a well bore that obviates or mitigates at least some of the disadvantages of the prior art.